The Material Corrosion Test (MaCoTe) Introduction
RWM, United Kingdom
Nuclear Waste Management Organization (NUMO), Japan
SURAO, Czech Republic
The Material Corrosion Test (MaCoTe) consists of non-heated and heated experiments to study in-situ corrosion of candidate canister materials embedded in bentonite.
Two broad aims are as follows:
- Provide confirmation of the long-term anaerobic corrosion rate of carbon steel, stainless steel and copper in compacted bentonite under repository-relevant environmental conditions,
- Provide experimental evidence of the inhibiting effect of the bentonite buffer on microbial activity and microbially-influenced corrosion.
Experimental Layout (non-heated test)
The current ongoing in-situ experiment is made up of a series of specially designed modules (0.3 m long) that are inserted into a 10m long vertical borehole and sealed with a double packer system. Each module contains 12 specimens embedded in MX-80 bentonite with dry densities of either 1.25 or 1.5 Mg/m3 (Figure 1)
Figure 1: Experimental layout: Borehole with modules; cutaway of one module showing the distribution of metal coupons.
The first eight modules were inserted into the borehole in September 2014. Retrieval will be made at increasingly longer intervals with the final two modules will be retrieved after 10 years.
MaCoTe non-heated test sampling plan (Phase 1: 2013 – 2018; Phase 2: 2019 – 2023). The vertical axis indicates the position of the module in the borehole. The bottom two modules (modules 7 and 8) will remain in the borehole for 10 years.
Corrosion rates of samples will be determined by weight loss method and the mineral alterations at the interfaces will be analyzed with available analytical methods (e.g. SEM-EDX, XRD, etc.). Microbial populations both in the bentonite and the borehole water will be analyzed using advanced cell counting and DNA mapping techniques.
In-situ heated corrosion test
The heated in-situ test will consist of 5 specially designed heater probes with rings made up of the target material (copper coatings and carbon steel), surrounded by bentonite rings and inserted into 5 boreholes. The duration of each test will be 1, 2, 3, 5 and 7 years and will start in July 2015.